1. Field of the Invention
The present invention relates to multi-hulled nautical vessels and to the design of hulls for multi-hulled nautical vessels. More particularly, this invention is directed to hulls for vessels of the type having at least three hulls which define a floating polygon having a longitudinal axis of symmetry and being capable of navigating as a hydroplane. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
Single-hull vessels intended to navigate under hydroplane conditions are, of course, well known. Such prior art vessels are typically driven by means of a propeller in such a manner that the thrust axis produces a torque tending to cause the hulls to "rear." When running at high speed a trim of balance is sought in which the buoyancy tends to be of a hydrodynamic rather than hydrostatic nature. However, the balance remains essentially dynamic at high speeds. Any fluctuations in the operating conditions, for example a variation in the thrust provided by the engine or a change in the reaction between the hull and the fluid medium as will be caused by choppy seas, will disturb the balance of the vessel. Any disturbance of balance will cause the vessel to dip and thus subject the hull to considerable shocks upon its re-decent into the water. As is well known, such shocks reduce the performance of the vessel and are liable to damage the hull. The lateral stability of prior art single-hull hydroplane vessels is also very mediocre and can only be improved through the use of longitudinal keel devices which, as is well known, have a deleterious effect on the main performance of the vessel. In the case of vessels employed for racing, the hulls are known to rear excessively to the point where the vessel may turn over and control is lost in turns at an excessive angular velocity.
Stepped hulls have previously been proposed in an effort to overcome the above briefly discussed deficiencies of prior art single-hull hydroplane vessels. The previously proposed stepped hulls, however, have not resulted in any improvement in lateral stability nor have they provided the requisite characteristics required for operation over rough seas.
The above discussed deficiencies of the prior art are an inherent result of the design configurations of prior art hulls. An analysis of a rectangular plate, partially immersed in liquid, may be considered to study the principle of hydroplane navigation and understand the problems of the prior art.
Referring to FIG. 1, a rectangular plate having a wetted surface area S is shown partially immersed in a liquid and is considered to be moving through the liquid from right to left as shown with a velocity V. L is the longitudinal length of the wetted (i.e. immersed) surface, 1 is the width of the immersed surface, C is the center of the thrust, and i is the angle of inclination of the plate with respect to the surface of the liquid. The plate exerts a reaction force K.sub.r, presenting a vertical component K.sub.y and a horizontal component K.sub.x. A rectangular plate with the surface S, entirely immersed in a liquid and moved perpendicularly in this liquid at the speed V will exert an antagonistic reaction force defined by: ##EQU1## a.sub.o representing the relation between the large and the small sides of the rectangle.
K.sub.o = 45 in the indicated system where S is expressed in sq.m, V in m/s and R in Kg.sub.f (kilogram force).
What happens in the case if a rectangular surface advances slantingly while only being partially immersed?
Let us assume a rectangular surface immersed under the conditions of FIG. 1, with the parameters explicit (except V, from right to left). Let us call a = 1/L the relation of the transversal side to the longitudinal side of the wet surface. C is the thrust center.
The reactive force, symbolized by K.sub.r, has a vertical component K.sub.y and a horizontal one K.sub.x. These terms correspond to the coefficients that, multiplied by SV.sup.2, give the corresponding component force, S being obviously the wetted surface only.